A variety of studies are proposed which will enhance our understanding of the nature of visual transduction. Particular attention will be paid to the changes which take place in visual pigments upon absorption of light which initiate the visual transduction process. This will be done on several levels. Photochemical processes in polyenes will be investigated because the initial step in transduction involves a photoisomerization of the retinal chromophore of visual pigments. Understanding what influences the isomerization process in polyenes will help us understand how this process is mediated in the protein. The photointermediates of both native and artificially modified visual pigments will also be studied. What intermediates are formed, how they transform into one another, and what properties they have will be studied by time-resolved absorption spectroscopy. Most of this work will be carried out on bovine rhodopsin and related pigments but the work will also be extended to the study of human rhodopsin. Recently, studies have linked some retinal diseases to a wide variety of specific mutations in the rhodopsin gene. This suggests that the functioning of rhodopsin is directly related to human visual disorders. It is thus important to understand the how rhodopsin functions. Studies of the bovine system are important as sufficient material is available to obtain a detailed understanding of the protein function. Extensions to the study of human rhodopsin are also important if we are to relate human visual disorders to rhodopsin function.